How To Test The iPhone Signal

Enter field test mode dial *3001#12345#* and press the call button. The phone will enter field test mode and your signal strength will change to a number.

Hold down the power/lock button until the power down display is on the screen. Press and hold the home button for about six seconds

The phone goes to your homescreen and the number stays. Tap the number to switch back and forth with the bars. The higher the number, the stronger the signal. Since the numbers are negative, a range between -40 and -77 is a good five bar signal. And one bar signal would be about -102 to -120.

Example

Office : -102

Office Roof : -70

Park : -70

Elevator : -113

Note - If you want to turn it off, enter the code again and it will be disabled.